Most modern engines are direct-injection engines, which means that each combustion cylinder of the engine includes a dedicated fuel injector configured to inject fuel directly into a combustion chamber. While direct-injection engines represent an improvement in engine technology over past designs, in the form of increased engine efficiency and reduced emissions, the improvement of the design of any particular engine is always desirable, especially in light of increasing fuel costs and ever more strict regulations on engine emissions.
In a traditional direct-injection engine, one or more fuel jets that are injected into a combustion chamber interact with various combustion chamber structures, which cause the fuel to disperse into the combustion chamber. More specifically, the fuel jet(s) entering the combustion chamber impact various surfaces of the combustion chamber such as a piston bowl, the flame deck surface of the cylinder head, the cylinder liner or bore, and other surfaces before spreading in all directions. The impingement of the fuel jets with these structures may have a variety of effects including increased emissions because localized areas having higher fuel concentrations may burn rich, while other areas on the cylinder may burn lean. Following interaction with the various internal surfaces of the cylinder, the fuel jets and resulting flames may also interact with neighboring fuel jets or flames. These interactions can further result in higher temperatures, decreased fuel efficiency, increased heat rejection and component temperatures, and the like.
Various solutions have been proposed in the past for improving an engine's efficiency and reducing its emissions. One example of a previously proposed solution can be seen in U.S. Pat. No. 8,646,428 (“Eismark”), which was granted on Feb. 11, 2014. Eismark describes a piston having a crown in which protrusions having a smooth form are adapted for preserving kinetic energy in a flame plume. The piston is designed to be used in an engine in which quiescent air is provided in the engine cylinder. The fuel injector, forms fuel jets or flames that impinge on features formed in the piston bowl to redirect portions of the flames upward, towards a cylinder head surface, and the remaining portions of the flames in a tangential direction, within the bowl, to achieve better mixing of the combustion gases and decrease or eliminate stagnation zones in a combustion chamber.
While the flow redirection of Eismark may be partially effective in improving burning of fuel in an engine cylinder, it is configured to operate with a quiescent cylinder, which is difficult to attain for each cylinder consistently. In a typical engine, the momentum of intake air into an engine cylinder will possess at least some swirl, which following fuel injection into the cylinder will cause the flames that develop to be carried by the swirling air to one side and generally towards the cylinder wall.